1. Field of the invention
The present invention relates to a color image scanner, and more particularly, to a color image scanning method of a color image scanner.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a perspective view of image scanning lines 16, 18 of a document 10. The scanning module 12 comprises a plurality of light sensors 14 arranged in a linear manner that are used to scan a document 10. The scanning module 12 scans the document 10 to sequentially produce image scanning lines 16, 18. In this way, a document image is formed. Each scanning line 16, 18 comprises a plurality of scanning dots that correspond to the output of the sensors 14. The inset denoted by a dotted square 30 shows an enlarged view of scanning lines 16, 18. The square 30 indicates that each scanning line 16, 18 has red image, green image, and blue image lines 22, 24, and 26. Although each of these image lines is close to each other, they are not precisely coincident. This is because the scanning module 12 advances at a constant speed and motion as it takes samples. This results in varying positions of each sample. The result is that each scanning point 20 of the scanning line 16 in effect comprises red, green and blue scanning points 32, 34, and 36. The samples are taken at a much faster speed than the movement of the sensors 14. Therefore, the red, green, and blue scanning points 32, 34, 36 are very close together and are viewed as a scanning point 20 thus forming the image of the scanned document.
Please refer to FIG. 2. FIG. 2 is a schematic diagram of intensity and time-sequence of three light sources 42, 44, 46 of a prior art color scanner. In the prior art the image line of each color is obtained by using the light source of that color. For example, to obtain an image scanning line, the red, green, and blue light sources 42, 44, and 46 are turned on sequentially to produce their respective image lines 22, 24, 26 in sequence. The scanning module 12 is then further driven to complete the scanning of the document 10. There are many methods to calibrate the image scanning line. The first method is to calibrate the image lines 22, 24, 26 before the composed image scanning line is outputted. The second method is to adjust intensities or turn-on periods of the three light sources 42, 44, 46 before scanning is performed. These methods only utilize the light source 42, 44, 46 of each color to obtain the respective image line 22, 24, 26.
It is therefore a primary objective of the present invention to provide a color image scanning method of a color image scanner to solve the above mentioned problems.
In a preferred embodiment, the present invention provides a color image scanning method of a color image scanner, the scanner comprising three light sources for emitting three different colored lights to illuminate a document to be scanned, and a scanning module for scanning the lights transmitted from the document to generate scanned color image signals of the document, the method comprising:
(1) using each of the three light sources and the scanning module to scan a color calibration document to obtain three sets of scanned color image signals of the color calibration document, where three sets of final color image signals of the color calibration document are known;
(2) using the three sets of scanned color image signals and final color image signals of the color calibration document to calculate three sets of color calibration parameters for calibrating the three light sources, each set of color calibration parameters comprising three color calibration parameters for calibrating the three light sources to obtain one set of final color image signals; and
(3) using each of the three sets of color calibration parameters to adjust the three light sources when scanning the document so as to obtain three sets of final color image signals of the document.
It is an advantage of the present invention that the scanning module scans the document using three light sources while also using calibrating parameters to obtain image scanning lines. Finally, the final scanning image is obtained by combining the image scanning lines.
This and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various figures and drawings.